1H-imidazo(4,5-b)pyridine compounds

ABSTRACT

Substituted 1-hydroxy-2-(1,1-difluoroalkyl)-1H-imidazo-(4,5-b)pyridine compounds useful as herbicides; and intermediates useful in the synthesis of these compounds. In addition to exhibiting herbicidal activity, the substituted 1-hydroxy-2-(1,1-difluoroalkyl)-1H-imidazo(4,5-b)pyridine compounds are of low mammalian toxicity.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of our copending application Ser. No.472,923, filed May 23, 1974, now abandoned. Application Ser. No. 472,923was in turn a continuation-in-part of our then copending applicationSer. No. 181,574, filed Sept. 17, 1971, and issued May 28, 1974 as U.S.Pat. No. 3,813,408. Application Ser. No. 181,574 was in turn acontinuation-in-part of our then copending application Ser. No. 21,535,filed Mar. 20, 1970 and abandoned after the filing of application Ser.No. 181,574.

SUMMARY OF THE INVENTION

The present invention is directed tosubstituted-1-hydroxy-2-(1,1-difluoroalkyl)-1H-imidazo(4,5-b)pyridinecompounds of the following formula: ##STR1## and the salts thereof. Inthe above and succeeding formulae throughout the present specificationand claims, R¹ represents hydrogen, chlorine, fluorine, difluoromethyl,perfluoroalkyl of C₁ -C₆, or radical of the formula ##STR2## whereineach Z independently represents hydrogen or halogen and m represents 0or 1; R² represents amino, halogen, nitro, cyano, loweralkyl of C₁ -C₄,perfluoroalkyl of C₁ -C₈, --CF₂ Cl, --CF₂ H, or loweralkylsulfonyl of C₁-C₄ ; and n represents an integer of from 1 to 3, both inclusive,subject to the limitations (1) that all R² substituents together containnot more than 8 carbon atoms; (2) that not more than two R² symbolsrepresent loweralkylsulfonyl groups; and (3) that where twoloweralkylsulfonyl groups are present they are located at the 5- and7-positions. These compounds are useful as herbicides. Hence, thepresent invention is also directed to methods employing and compositionscomprising the compounds as herbicides. The above-described compoundsare also useful as starting materials from which other of theabove-described compounds can be prepared.

In addition, the present invention is also directed to various separateclasses of intermediates useful in the preparation of the compoundsdefined above, including the most intermediate precursors of theformulae: ##STR3## wherein R¹ and R² are as defined above, and ##STR4##wherein R³ represents loweralkylsulfonyl of C₁ -C₄, both inclusive.

DETAILED DESCRIPTION OF THE INVENTION

In the present specification and claims, the term "halogen" is employedto designate bromine, chlorine, fluorine, and iodine, only.

An essential and distinguishing structural feature of the compounds ofthe present invention is the substituent at the 2 position (--CF₂ -R¹);representative such radicals include the following:

difluoromethyl

trifluoromethyl

difluorochloromethyl

pentafluoroethyl

heptafluoro-n-propyl

1,1-difluoroethyl

1,1-difluoro-n-propyl

1,1-difluoro-2-bromoethyl

1,1-difluoro-2-chloroethyl

1,1-difluoro-2,3-dichloro-n-propyl

1,1-difluoro-3-bromo-n-propyl

1,1,2-trifluoroethyl

1,1,2-trifluoro-n-propyl

1,1,2,3-tetrafluoro-n-propyl

1,1-difluoro-2-bromo-3-chloro-n-propyl

perfluoro-n-butyl

perfluoro-n-pentyl

perfluoro-n-hexyl

1,1,2,2,-tetrafluoroethyl

Preferred groups are trifluoromethyl, difluoromethyl, difluorochloromethyl, 1,1,2,2-tetrafluoroethyl, and pentafluoroethyl.

The compounds of the present invention are typically crystalline solids.Two synthetic routes are useful in the preparation of the compounds. Thefirst of these is as follows: ##STR5##

In accordance with the foregoing reaction route, the initialsubstituted-2-amino-3-nitropyridine compound is acylated to yield thecorresponding substituted-2-(2,2-difluoroalkanamido)-3-nitropyridine,which is then reacted further to yield the final product in accordancewith the present invention. Because of the ready availability ofsuitable starting materials, this reaction scheme is particularly suitedto the preparation of the mono-substituted compounds of the presentinvention. Where suitable starting materials are available, it isequally suited to the preparation of di- and tri-substituted compounds.However, the di- and tri-substituted compounds are often preferablyprepared in an alternate synthetic route, discussed below.

In the synthetic route described above, the acylation is carried outwith an acylating agent, the identity of which is not critical; eitherthe difluoroalkanoyl halide: ##STR6## or the difluoroalkanoic anhydride##STR7## is suitable, although the latter is often preferred. Ingeneral, the reaction is conducted by mixing the acylating agent and thesubstituted-3-nitro-2-aminopyridine. In the case of a difluoroalkanoylhalide, the use of an acid accepting amide or organic tertiary amine ispreferred. Particularly suited organic tertiary amines includetriethylamine and pyridine; and suitable amides include DMF anddimethylacetamide. The reaction goes forward at temperatures of from25°-100° C. and can be conducted in an inert liquid reaction medium,such as benzene; or an excess of the organic tertiary amine can beemployed as reaction medium; in addition, the difluoroalkanoicanhydrides are generally liquid, and an excess amount can be used toassure fluidity. The reaction goes forward readily yielding the desiredsubstituted-3-nitro-2-(2,2-difluoroalkanamido)pyridine product.Separation of the product, and, if desired, purification are carried outin conventional procedures.

The reaction of the resultingsubstituted-3-nitro-2-(2,2-difluoroalkanamido)pyridine to prepare theultimate products of the present invention, is in part the subject ofcopending application Ser. No. 21,226, filed Mar. 19, 1970. In general,it has been found that subjecting the substituted-3-nitro-2-(2,2-difluoroalkanamido)pyridine compounds, as well as othercompounds, to any of a variety of reducing conditions results in thepreparation of the ultimatesubstituted-1-hydroxy-2-(1,1-difluoroalkyl)-1H-imidazo(4,5-b)pyridinecompounds of the present invention. It is believed that the reactionproceeds through an intermediate: ##STR8##

To date, it has not been possible to isolate this intermediate. As willbe obvious to those skilled in the art, however, the intermediate, ifisolatable from any synthetic route, could itself be reacted to producethe compounds of the present invention.

While the reaction itself is unexpected, the reaction conditions are notcritical. As reducing agent, there can be employed, for example, any ofthe substances and conditions ordinarily employed for the reduction ofnitro compounds to amino compounds: hydrogen in the presence of acatalyst; zinc or iron in acid solution; sulfides in alkaline solution;hydrosulfite in alkaline solution; and the like. The reactions areconducted in accordance with the conditions known for each of theseagents (see Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Ed.,Vol. 2, pages 76-98 and references there cited [John Wiley and Sons,Inc., 1963, New York]); and in all instances, cyclodehydration of theintermediate occurs spontaneously under such reducing conditions.

However, a preferred method for conducting the reduction reaction is theuse of hydrogen in the presence of a catalyst. In general, in employingthis preferred method, thesubstituted-3-nitro-2-(2,2-difluoroalkanamido)pyridine, conveniently inan inert liquid as reaction medium, is subjected to hydrogenation in thepresence of catalyst, typically a noble metal and preferably palladiumor platinum. The catalyst can be employed alone, or--especially in theinstance of palladium--can be supported on a carrier such as carbon oran alkali metal salt. Conveniently, a Parr or other pressure apparatusis used to contain the reaction mixture during hydrogenation, whenconducted at superatmospheric pressures; however, the reaction also goesforward at atmospheric pressures. The reaction is further catalyzed by asmall amount of an acid, such as, for example, a mineral acid such ashydrochloric acid or a compatible organic acid such as trifluoroaceticacid.

The amounts of reactants employed are not critical. In general,preferred amounts of 2 moles of hydrogen per mole of the startingsubstituted-3-nitro-2-(2,2-difluoroalkanamido)pyridine and a catalyticamount of the noble metal, such as from 1 to 10 grams per kilogram ofthe starting compound. Temperatures of from 0° to 100° C. are operative,but better results are typically achieved at temperatures of from 10° to25° C.

When hydrogen uptake is complete, the product is separated from thereaction mixture in conventional procedures. Most typically, thereaction mixture is filtered to remove remaining catalyst, and thefiltrate evaporated to separate the product as a residue. This productresidue can be purified, also in conventional procedures, typicallyrecrystallization, or extraction into sodium bicarbonate solutionfollowed by precipitation with mineral acid.

In an alternate synthetic route, a suitably substituted 1-hydroxycompound of the present invention is itself used as a starting materialfor the preparation of other of the compounds of the present invention.This synthetic route is particularly suited to the preparation of thepoly substituted compounds of the present invention (n = 2 or 3) wherethe necessary starting material for the first synthetic route is notreadily available. The 1-hydroxy compound is subjected to reactions tointroduce onto the pyridine ring one or more desired groups and/or toconvert one or more substituents already present on the pyridine ring tothe desired group or groups.

Thus, for example, the 1-hydroxy compound serving as starting materialfor this synthetic route can be halogenated or nitrated at a position orpositions previously unsubstituted. A nitro group already present can bereduced to an amino group; and an amino group already present can alsobe oxidized back to a nitro group. An amino group can also be diazotizedand replaced by, for example, a halo group, a nitrile group, or aloweralkylthio group. Oxidation of the loweralkylthio-substitutedcompound yields the corresponding loweralkylsulfonyl-substitutedcompound. The fluorinated groups (R² = --CF₃, --CF₂ Cl, or --CF₂ H) arereadily obtained, initially by conversion of a nitrile to a carboxylgroup; subsequent treatment with SF₄ in the presence of HF yields the--CF₃ group. Alternately, conversion to an aldehyde and treatment withSF₄ alone yields the --CF₂ H group; and subsequent chlorination convertsthe --CF₂ H group to the corresponding --CF₂ Cl group. An alkylsubstituent is introduced by reaction of an alkyl lithium with ahalo-substituted 1-hydroxy compound; and a perfluoroalkyl substituent sintroduced by reaction of a halo-substituted 1-hydroxy compound with aperfluoroalkyl iodide in the presence of copper. This and numerous otherconversion and substitution reactions are well known to those skilled inthe art. Attention is directed to Fieser and Fieser, Advanced OrganicChemistry (Reinhold Publishing Corp., New York, N.Y., 1961), especiallychapters 9 and 17. See also Wagner and Zook, Synthetic Organic Chemistry(John Wiley and Sons, Inc., New York, N.Y., 1953).

As will be understood by those skilled in the art, more then one of theforegoing reactions will be needed to complete the preparation of someof the compounds of the present invention; and in the case of allreactions, due consideration must be given to the orienting effect ofsubstituent groups. Also, for those of the foregoing reactions whichutilize a nucleophilic reagent, it may be necessary that the 1-hydroxygroup be converted to an ester or ether. Conversion is readily achievedby reacting the 1-hydroxy compound with an alkyl halide or an acylhalide in the presence of a hydrogen chloride acceptor. The identity ofthe alkyl halide or acyl halide is not critical: suitable compoundsinclude the methyl halides and the acetyl halides. An ester derivativeis converted back to the 1-hydroxy compound in conventional procedures.

The foregoing synthetic methods result in the preparation of the desiredsubstituted-1-hydroxy-2-(1,1-difluoroalkyl)-1H-imidazo(4,5-b)pyridinecompounds of the present invention. However, the proton of the OH groupbeing acidic, these compounds form salts with cations. Representativesuch salts include salts with alkali metals, such as sodium, potassium,lithium, cesium, and rubidium; alkaline earth metal salts, such ascalcium, strontium, and barium salts; and salts with organic amines.While the identity of the organic amine is not critical, preferredorganic amines are those which have relatively high base strength, suchas a dissociation constant (K_(b)) of the order of 10⁻⁵ or greater. Ingeneral, the alkylamines, cycloalkylamines, alkylenepolyamines, andaralkylamines are classes of compounds exhibiting adequate basestrengths. Thus, representative bases include methylamine,dimethylamine, trimethylamine, methyldiethylamine, ethylamine,diethylamine, triethylamine, n-propylamine, di-n-propylamine,tri-n-propylamine, n-amylamine, cyclohexylamine, piperidine,pyrrolidine, N-methylpyrrolidine, diisopropylamine, ethylenediamine,tetramethylenediamine, ethanolamine, benzylamine, isobutylamine,di-n-butylamine, and the like. The foregoing salts are prepared inconventional procedures, by reaction of the 6-substituted1-hydroxy-2-(1,1-difluoroalkyl)imidazo(4,5-b)pyridine and the particularamine or alkali metal or alkaline earth metal oxide, hydroxide, or salt.Such salt formation can be employed as a method of formulating thesubject compounds.

The following examples illustrate the present invention and will enablethose skilled in the art to practice the same.

EXAMPLE 1 5-CHLORO-3-NITRO-2-(TRIFLUOROACETAMIDO)PYRIDINE

5-Chloro-3-nitro-2-aminopyridine (5.0 grams) and excess trifluoroaceticanhydride were refluxed together for 24 hours. TLC showed no reactionhad taken place. Pyridine (2.0 ml.) was then added. After fifteenminutes the solution solidified. The product was dissolved in chloroformand washed twice with water, and the chloroform was then evaporatedunder vacuum. The resulting product residue was recrystallized from amixture of benzene and aliphatic naphtha: m.p., 104°-05° C., yield 6.0g.

Analysis, Calc.: C, 31.20; H, 1.12; N, 15.59. Found: C, 32.20; H, 1.44;N, 15.83.

EXAMPLE 2 5-CHLORO-3-NITRO-2-(TRIFLUOROACETAMIDO)PYRIDINE

The compound of Example 1 was also synthesized by dissolving the5-chloro-3-nitro-2-aminopyridine (5.0 grams) in a minimum amount of warmtrifluoroacetic acid, and then adding 1.5 equivalents of trifluoroaceticanhydride and 0.5 milliliters of pyridine and refluxing for about anhour. The reaction mixture was then poured onto ice to precipitate the5-chloro-3-nitro-2-(trifluoroacetamido)pyridine compound, which wasseparated, dissolved in chloroform, and washed twice with water.Thereafter, the solution was shaken with activated carbon and filtered,and chloroform removed under vacuum to obtain a purified product. It wasfurther recrystallized from a low boiling (40°-50° C.) petroleum ether,m.p., 104°-05° C.

EXAMPLE 3 5-(TRIFLUOROMETHYL)-3-NITRO-2-(TRIFLUOROACETAMIDO)PYRIDINE

5-(Trifluoromethyl)-3-nitro-2-aminopyridine (2.0 grams) was mixed with10 milliliters of pyridine and 1 milliliter of trifluoroacetic anhydrideadded with cooling. After 30 minutes, the reaction mixture was heated to100° C. and maintained thereat for 10 minutes. The reaction mixture wasthen poured into ice and hydrochloric acid (of a concentration of 50grams of ice per 10 milliliters of hydrochloric acid). The reactionmixture was then filtered and the resulting residue, the desired5-(trifluoromethyl)-3-nitro-2-(trifluoroacetamido)pyridine, taken up inchloroform, dried, and solvent evaporated to obtain a purified product.It was further recrystallized from benzene, m.p., 68°-70° C.

EXAMPLE 4 5-(METHYLSULFONYL)-3-NITRO-2-(TRIFLUOROACETAMIDO)PYRIDINE

5-(Methylsulfonyl)-3-nitro-2-aminopyridine (2.0 grams) was mixed with 15milliliters of trifluoroacetic anhydride and 4 milliliters of pyridine.The resulting mixture was stirred under reflux until the reactionmixture changed color, from gray to dark brown, and began solidifying.An additional 10 milliliters of the trifluoroacetic anhydride was thenadded and the reaction mixture refluxed for another hour. The excessanhydride was then removed by evaporation, yielding the desired5-(methylsulfonyl)-3-nitro-2-(trifluoroacetamido)pyridine. It wasdissolved in chloroform, washed once with water, and dried overmagnesium sulfate; the chloroform was then removed by evaporation, andthe resulting product was recrystallixed from benzene/acetone, m.p.,159°-61° C.

Analysis, Calc.: C, 30.67; H, 1.93; N, 13.42. Found: C, 30.73; H, 2.00;N, 13.58.

EXAMPLE 5 1-HYDROXY-2,6-BIS(TRIFLUOROMETHYL)-1H-IMIDAZO-(4,5-b)PYRIDINE

5-(Trifluoromethyl)-3-nitro-2-aminopyridine (10.0 grams) intrifluoroacetic anhydride (10 ml.) and pyridine (20 ml.) were heated ina steam bath for 2 hours. Solvents were then evaporated on a rotaryevaporator at 100° C. for one hour, and the residue was taken up inethyl acetate and hydrogenated over 2.0 g. of 5 percent palladium oncarbon. The reaction mixture was then filtered, evaporated, and taken upin ethanol; subsequently, the mixture was washed with 10 percenthydrochloric acid, dried over magnesium sulfate, and evaporated. Theresulting 1-hydroxy-2,6-bis(trifluoromethyl)-1H-imidazo(4,5-b)pyridineproduct was recrystallized from acetone, m.p., 239°-40° C.

Analysis, Calc.: C, 35.44; H, 1.15; N, 15.50; F, 42.05. Found: C, 35.40;H, 1.43; N, 15.28; F, 42.32.

EXAMPLE 66-CHLORO-1-HYDROXY-2-(TRIFLUOROMETHYL)-1H-IMIDAZO(4,5-b)PYRIDINE

5-Chloro-3-nitro-2-(trifluoroacetamido)pyridine (2.0 grams) washydrogenated with two moles of hydrogen in ethanol containing 0.5 gramof 5 percent palladium on carbon. The resulting reaction mixture wasfiltered and evaporated to separate the desired6-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridinecompound which, after recrystallization from benzene melted at 268°-70°C.

Analysis, Calc.: C 35.39; H, 1.27; N, 17.69. Found: C, 35.59; H, 1.45;N, 17.77.

EXAMPLE 7 6-CHLORO-1-HYDROXY-2-(TRIFLUOROMETHYL)IMIDAZO(4,5-b)PYRIDINE

5-Chloro-3-nitro-2-(trifluoroacetamido)pyridine (2.7 grams), anhydrousstannous chloride (3.8 grams), and 4.0 milliliters of concentratedhydrochloric acid were mixed in 20 milliliters of acetic acid. Themixture was cooled to temperatures of 0°-10° C. and maintained thereatfor 15 minutes. Water (50 milliliters) was then added to the reactionmixture, and the desired6-chloro-1-hydroxy-2-(trifluoromethyl)imidazo(4,5-b)pyridine productprecipitated. It was separated and dried. The yield was 1.3 grams, 55percent. The product so obtained melted at 264°-66° C.

EXAMPLE 86-CHLORO-1-HYDROXY-2-(TRIFLUOROMETHYL)-1H-IMIDAZO-(4,5-b)PYRIDINETRIETHYLAMINE SALT

6-Chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine (1gram) was mixed with 15 milliliters of tetrahydrofuran, and 0.7milliliter of triethylamine added. The reaction mixture was evaporatedand then held in a vacuum desiccator overnight, resulting in the desired6-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridinetriethylamine salt. The compound was subjected to NMR analysis (indeuterium oxide); analysis showed a triplet centered at 82 cps (9H); aquartet centered at 196 cps (6H); a meta-coupled doublet at 400 cps(1H); and a second meta-coupled doublet centered at 503 cps (1H).

EXAMPLE 96-CHLORO-1-HYDROXY-2-(TRIFLUOROMETHYL)-1H-IMIDAZO(4,5-b)PYRIDINEBENZYLAMINE SALT

6-Chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine (1.4grams) was mixed with 15 milliliters of ethyl acetate. The mixture washeated to reflux, and 0.6 milliliter of benzylamine was added dropwise.The mixture was then refluxed for another 30 minutes, cooled, andfiltered, yielding the desired6-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridinebenzylamine salt, m.p., 200°-02° C. NMR analysis in hexadeuterodimethylsulfoxide showed a peak at 236 cps (2H); a peak at 437 cps (5H); twometa-coupled doublets at the 462 cps (1H), the other at 500 cps (1H);and a broad peak at 474 cps (3H).

Analysis, Calc.: C, 48.75; H, 3.51; N, 16.25. Found: C, 48.52; H, 3.72;N, 16.07.

EXAMPLE 106-AMINO-1-HYDROXY-2-(TRIFLUOROMETHYL)-1H-IMIDAZO-(4,5-b)PYRIDINE

6-Nitro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine (4.9grams) was mixed with 100 milliliters of ethanol and 3 milliliters ofconcentrated hydrochloric acid, and 1 gram of 5 percent palladium oncarbon was added to the mixture. The mixture was hydrogenated to a 3mole-equivalent uptake of hydrogen. The reaction mixture was thenfiltered and evaporated, yielding a gummy solid residue which was takenup in 150 milliliters of water and used directly in the reactionreported in the following example.

EXAMPLE 115,7-DIBROMO-6-AMINO-1-HYDROXY-2-(TRIFLUOROMETHYL)-1H-IMIDAZO(4,5-b)PYRIDINE

The aqueous solution of6-amino-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine obtainedas reported in the preceding example was treated with 2.2 milliliters ofbromine in an N₂ --H₂ O stream. Thereafter the reaction mixture wasstirred for sixteen hours under nitrogen. The desired5,7-dibromo-6-amino-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridineprecipitated in the reaction mixture and was separated by filtration. Itwas taken up in 250 milliliters of diethyl ether, stirred for one hour,dried over magnesium sulfate, and filtered. The diethyl ether wasevaporated to give 3.4 grams of the desired product in purified form,m.p., 242°-4° C. (dec.).

EXAMPLE 125,7-DIBROMO-6-NITRO-1-HYDROXY-2-(TRIFLUOROMETHYL)-1H-IMIDAZO(4,5-b)PYRIDINE

5,7-Dibromo-6-amino-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine(25 milligrams) was added to a stirred solution of 2 milliliters of 30percent hydrogen peroxide and 5 milliliters of sulfuric acid at about 5°C. The reaction mixture was allowed to come to 25° C. and permitted tostand for one hour. The reaction mixture was then diluted with icewater, extracted with diethyl ether, and dried over magnesium sulfate,and the ether evaporated leaving a residue, the desired5,7-dibromo-6-nitro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine.It was recrystallized from chloroform, m.p., 204° C. (dec.).

EXAMPLE 13 DIAZONIUM SALT DERIVED FROM1,5-DIHYDROXY-7-BROMO-6-DIAZO-2-(TRIFLUOROMETHYL)-1H-IMIDAZO(4,5-b)PYRIDINE

5,7-Dibromo-6-amino-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine(1.2 grams) in 7 milliliters of concentrated hydrochloric acid wascooled with stirring to about 10° C. Sodium nitrite (0.35 gram) in 2.0milliliters of water was then added dropwise with stirring and thereaction mixture was stirred at ambient temperature of about 25° C. forabout sixteen and one-half hours. The reaction mixture was then dilutedwith water and filtered to separate a solid, the desired diazonium saltderived from1,5-dihydroxy-7-bromo-6-diazo-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine.It was promptly analyzed by IR, which showed a peak at 2.80, confirmingthe N.tbd.stretch, and a low (1630-1640) carbonyl absorption. Theformula of this diazonium salt is as follows: ##STR9##

EXAMPLE 145,7-DIBROMO-6-CHLORO-1-HYDROXY-2-(TRIFLUOROMETHYL)-1H-IMIDAZO(4,5-b)PYRIDINE

5,7-Dibromo-6-amino-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine(1.2 grams) in 7 milliliters of concentrated HCl was cooled to 0°-10° C.Thereafter, sodium nitrite (0.35 gram) was added as a solid. Theaddition was carried out portionwise to maintain the temperature below10° C. Five minutes after completion of the addition of the sodiumnitrite, cuprous chloride (0.45 gram) was added portionwise and theresulting reaction mixture stirred for thirty minutes and filtered toseparate the desired5,7-dibromo-6-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridineproduct, m.p., 215° C.

Analysis, Calc.: C, 21.27; H, 0.25; N, 10.63. Found: C, 21.50; H, 0.50;N, 11.10.

EXAMPLES 15-47

Other products of the present invention are prepared in accordance withthe procedures and teachings hereinabove. Representative such otherproducts include the following:

3,5-Dinitro-2-aminopyridine is reacted with difluoroacetic anhydride toobtain 3,5-dinitro-2-(difluoroacetamido)pyridine, which in turn ishydrogenated in the presence of platinum to obtain6-nitro-1-hydroxy-2-(difluoromethyl)-1H-imidazo(4,5-b)pyridine.

5-Bromo-3-nitro-2-aminopyridine is treated with chlorodifluoroaceticanhydride to yield 5-bromo-3-nitro-2-(chlorodifluoroacetamido)pyridine,which on hydrogenation in the presence of palladium on barium sulfate,yields6-bromo-1-hydroxy-2-(chlorodifluoromethyl)-1H-imidazo(4,5-b)pyridine.

5-Ethylsulfonyl-3-nitro-2-aminopyridine is reacted with trifluoroaceticanhydride to obtain5-ethylsulfonyl-3-nitro-2-(trifluoroacetamido)pyridine, which onhydrogenation in the presence of palladium on carbon yields6-ethylsulfonyl-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine.

5-Chloro-3-nitro-2-aminopyridine is treated with pentafluoropropionicanhydride to obtain5-chloro-3-nitro-2-(pentafluoropropionamido)pyridine, which whenhydrogenated in the presence of palladium on carbon yields6-chloro-1-hydroxy-2-(pentafluoroethyl)-1H-imidazo(4,5-b)pyridine, m.p.,240°-42° C.

5-(Chlorodifluoromethyl)-3-nitro-2-aminopyridine is reacted withheptafluorobutyric anhydride to obtain5-(chlorodifluoromethyl)-3-nitro-2-(heptafluorobutyramido)pyridine,which on hydrogenation in the presence of palladium on calcium sulfateyields6-(chlorodifluoromethyl)-1-hydroxy-2-(heptafluoropropyl)-1H-imidazo(4,5-b)pyridine.5-(n-Butylsulfonyl)-3-nitro-2-aminopyridine is reacted withtrifluoroacetic anhydride to obtain5-(n-butylsulfonyl)-3-nitro-2-(trifluoroacetamido)pyridine, which onhydrogenation in the presence of platinum yields6-(n-butylsulfonyl)-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine.

5-(Difluoromethyl)-3-nitro-2-aminopyridine is reacted withdifluoroacetic anhydride to obtain5-(difluoromethyl)-3-nitro-2-(difluoroacetamido)pyridine, which whenhydrogenated in the presence of palladium on barium sulfate yields2,6-bis(difluoromethyl)-1-hydroxy-1H-imidazo(4,5-b)pyridine.

5-(Methylsulfonyl)-3-nitro-2-aminopyridine is reacted withtrifluoroacetic anhydride to obtain5-(methylsulfonyl)-3-nitro-2-(trifluoroacetamido)pyridine which whenhydrogenated yields6-(methylsulfonyl)-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine,m.p., 265°-68° C.

Analysis, Calc.: C, 34.17; H, 2.15; N, 14.94. Found: C, 34.27; H, 2.37;N, 15.07.

5-Chloro-3-nitro-2-aminopyridine is reacted with heptafluorobutyricanhydride to obtain 5-chloro-3-nitro-2-(heptafluorobutyramido)pyridinewhich when hydrogenated yields6-chloro-1-hydroxy-2-(heptafluoro-n-propyl)-1H-imidazo(4,5-b)pyridine.

5-Chloro-3-nitro-2-aminopyridine is reacted with 2,2-difluoropropionicanhydride to obtain5-chloro-3-nitro-2-(2,2-difluoropropionamido)pyridine, which onhydrogenation in the presence of palladium on calcium sulfate yields6-chloro-1-hydroxy-2-(1,1-difluoroethyl)-1H-imidazo(4,5-b)pyridine.

5-(Trifluoromethyl)-3-nitro-2-aminopyridine is reacted with2,2-difluoro-3-bromopropionic anhydride to obtain5-(trifluoromethyl)-3-nitro-2-(2,2-difluoro-3-bromopropionamido)pyridine,which on hydrogenation in the presence of platinum yields6-(trifluoromethyl)-1-hydroxy-2-(1,1-difluoro-2-bromoethyl)-1H-imidazo(4,5-b)pyridine.

5-Iodo-3-nitro-2-aminopyridine is reacted with 2,2-difluorobutyricanhydride to obtain 5-iodo-3-nitro-2-(2,2-difluorobutyramido)pyridine,which when hydrogenated in the presence of palladium on barium sulfateyields6-iodo-1-hydroxy-2-(1,1-difluoro-n-propyl)-1H-imidazo(4,5-b)pyridine.

5-(Methylsulfonyl)-3-nitro-2-aminopyridine is reacted with2,2-difluoro-3,4-dichlorobutyric anhydride to obtain5-(methylsulfonyl)-3-nitro-2-(2,2-difluoro-3,4-dichlorobutyramido)pyridinewhich when hydrogenated yields6-(methylsulfonyl)-1-hydroxy-2-(1,1-difluoro-2,3-dichloro-n-propyl)-1H-imidazo(4,5-b)pyridine.

5-Fluoro-3-nitro-2-aminopyridine is reacted with2,2,3-trifluoropropionic anhydride to obtain5-fluoro-3-nitro-2-(2,2,3-trifluoropropionamido)pyridine which onhydrogenation over palladium on carbon yields6-fluoro-1-hydroxy-2-(1,1,2-trifluoroethyl)-1H-imidazo(4,5-b)pyridine.

5-(Trifluoromethyl)-3-nitro-2-aminopyridine is reacted with2,2-difluoro-4-iodobutyric anhydride to obtain5-(trifluoromethyl)-3-nitro-2-(2,2-difluoro-4-iodobutyramido)pyridine,which on hydrogenation yields6-(trifluoromethyl)-1-hydroxy-2-(1,1-difluoro-3-iodo-n-propyl)-1H-imidazo(4,5-b)pyridine.

5-Chloro-3-nitro-2-aminopyridine is reacted with perfluorooctanoicanhydride to obtain5-chloro-3-nitro-2-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentafluorooctanamido)pyridine,which on hydrogenation yields6-chloro-1-hydroxy-2-(perfluoro-n-heptyl)-1H-imidazo(4,5-b)pyridine.This compound is reacted with dimethylamine to obtain the dimethylaminesalt thereof.

5-(Trifluoromethyl)-3-nitro-2-aminopyridine is reacted withperfluorobutyryl chloride to yield5-(trifluoromethyl)-3-nitro-2-(2,2,3,3,4,4,4-heptafluorobutyramido)pyridine,which when hydrogenated yields6-(trifluoromethyl)-1-hydroxy-2-(perfluoro-n-propyl)-1H-imidazo(4,5-b)pyridine.

6-(Chlorodifluoromethyl)-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridineis reacted with pyridine to obtain the pyridine salt thereof.

6-(Methylsulfonyl)-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine,in a dilute aqueous solution of sodium hydroxide, forms the sodium saltthereof in solution.

6-Nitro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine isreacted with an aqueous solution of calcium carbonate, yielding thecalcium salt thereof. 6-Chloro-3-nitro-2-aminopyridine is reacted withtrifluoroacetic anhydride to obtain6-chloro-3-nitro-2-(trifluoroacetamido)pyridine, which when hydrogenatedyields 5-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine,m.p., 216° C. (dec.).

Analysis, Calc.: C, 35.39; H, 1.27; N, 17.69. Found: C, 35.60; H, 1.48;N, 17.96.

4-Chloro-3-nitro-2-aminopyridine is reacted with trifluoroaceticanhydride to obtain 4-chloro-3-nitro-2-(trifluoroacetamido)pyridine,which when hydrogenated yields7-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine, m.p.,170°-1° C.

5-Chloro-1-hydroxy-2-(pentafluoroethyl)-1H-imidazo(4,5-b)pyridine isreacted with methanethiol to obtain5-(methylthio)-1-hydroxy-2-(pentafluoroethyl)-1H-imidazo(4,5-b)pyridinewhich is subsequently oxidized to obtain the corresponding5-(methylsulfonyl)-1-hydroxy-2-(pentafluoroethyl)-1H-imidazo(4,5-b)pyridine.

7-Chloro-1-hydroxy-2-(difluoromethyl)-1H-imidazo(4,5-b)pyridine isreacted with sodium fluoride to obtain7-fluoro-1-hydroxy-2-(difluoromethyl)-1H-imidazo(4,5-b)pyridine, whichis then converted to its calcium salt.

5-Chloro-1-hydroxy-2-(1,1,2,2-tetrafluoroethyl)-1H-imidazo(4,5-b)pyridineis brominated to obtain5-chloro-6-bromo-1-hydroxy-2-(1,1,2,2-tetrafluoroethyl)-1H-imidazo(4,5-b)pyridine,which is then converted to its sodium salt.

7-Chloro-1-hydroxy-2-(difluorochloromethyl)-1H-imidazo-(4,5-b)pyridineis reacted with ammonium hydroxide to obtain7-amino-1-hydroxy-2-(difluorochloromethyl)-1H-imidazo(4,5-b)pyridinewhich is oxidized to the corresponding7-nitro-1-hydroxy-2-(difluorochloromethyl)-1H-imidazo(4,5-b)pyridine.Also, the7-amino-1-hydroxy-2-(difluorochloromethyl)-1H-imidazo(4,5-b)pyridine istreated with sodium nitrite and subsequently sodium cyanide to obtainthe corresponding7-cyano-1-hydroxy-2-(difluorochloromethyl)-1H-imidazo(4,5-b)pyridine. Ontreatment with 70 percent sulphuric acid the corresponding7-carboxy-1-hydroxy-2-(difluorochloromethyl)-1H-imidazo(4,5-b)pyridineis prepared. On further treatment with SF₄ and HF, there is obtained7-(trifluoromethyl)-1-hydroxy-2-(difluorochloromethyl)-1H-imidazo(4,5-b)pyridine.

6-Amino- 1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine isnitrated to obtain6-amino-5,7-dinitro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridinewhich is subsequently oxidized to obtain the corresponding5,6,7-trinitro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine.

6-Amino-1-hydroxy-2-(difluoromethyl)-1H-imidazo(4,5-b)pyridine ischlorinated to obtain6-amino-5,7-dichloro-1-hydroxy-2-(difluoromethyl)-1H-imidazo(4,5-b)pyridine.This compound is diazotized and treated with cuprous chloride to convertit to5,6,7-trichloro-1-hydroxy-2-(difluoromethyl)-1H-imidazo(4,5-b)pyridine.

5,6-Diamino-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine isdiazotized and subsequently reacted with cuprous cyanide to obtain thecorresponding5,6-dicyano-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine. Itis converted to the corresponding 5,6-dicarboxy compound by treatmentwith 70 percent sulfuric acid. Subsequent reaction of the5,6-dicarboxy-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridinewith SF₄ in the presence of HF yields the corresponding2,5,6-tris(trifluoromethyl)-1-hydroxy-1H-imidazo(4,5-b)pyridine.Rosenmund reduction of the 5,6-bis-acid chloride gives the dialdehydewhich is reacted with SF₄ to obtain5,6-bis(difluoromethyl)-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine.In turn, this compound is chlorinated to obtain5,6-bis(difluorochloromethyl)-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine.

6-Amino-5,7-dinitro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridineis diazotized and the diazo group subsequently removed entirely byreduction with hypophosphorous acid. The resulting5,7-dinitro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine ishydrogenated to the corresponding5,7-diamino-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine.This compound is diazotized and subsequently reacted with the sodiumsalt of methyl mercaptan to obtain5,7-bis(methylthio)-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridinewhich is oxidized to the corresponding5,7-bis(methylsulfonyl)-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine.

5-Chloro-3-nitro-2-aminopyridine is reacted with2,2,3,3-tetrafluoropropionyl chloride to yield5-chloro-3-nitro-2-(2,2,3,3-tetrafluoropropionamido)pyridine, which whenhydrogenated yields6-chloro-1-hydroxy-2-(1,1,2,2-tetrafluoroethyl)-1H-imidazo(4,5-b)pyridine.This compound is reacted with trimethylamine to prepare6-chloro-1-hydroxy-2-(1,1,2,2-tetrafluoroethyl)-1H-imidazo(4,5-b)pyridinetrimethylamine salt.

5-Methyl-3-nitro-2-aminopyridine is reacted with trifluoroaceticanhydride to obtain 5-methyl-3-nitro-2-(trifluoroacetamido)pyridine,which when hydrogenated yields6-methyl-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine, m.p.,275° C.

5-(Perfluorooctyl)-3-nitro-2-aminopyridine is reacted with2,2,3,3-tetrafluoropropionyl chloride to obtain5-(perfluorooctyl)-3-nitro-2-(2,2,3,3-tetrafluoropropionamido)pyridine,which when hydrogenated yields6-(perfluorooctyl)-1-hydroxy-2-(1,1,2,2-tetrafluoroethyl)-1H-imidazo(4,5-b)pyridine.

The compounds of the present invention are adapted to be employed asherbicides. The compounds can be utilized to achieve broad herbicidalaction; hence, in its broadest sense, the present invention is directedto a method which comprises applying to a plant part, which can be astem, leaf, flower, fruit, root, or seed or other similar reproductiveunit of a plant, a growth-inhibiting amount of one of thesubstituted-1-hydroxy-2-(1,1-difluoroalkyl)-1H-imidazo(4,5-b)pyridinecompounds of the present invention or one of the defined salts thereof.However, the compounds can also be utilized to take advantage ofselective patterns of herbicidal activity.

It is not critical to the practice of the present invention thatcomplete destruction of undesirable vegetation be obtained, it beingadequate if the growth of the unwanted vegetation is merely inhibited.Especially where selective action is sought, inhibition falling short ofactual killing is adequate, particularly when combined with naturallyoccurring conditions such as limited moisture and the like which moreadversely affect the vegetation selectively inhibited than the cropplant.

The compounds of the present invention are suited to a wide variety ofherbicidal applications. Thus, for example, at rates which evoke theselective action of the compounds, which rates are defined morecompletely hereinbelow, the compounds can be used as selectiveherbicides in crop plants, such as, for example, cotton, corn, sorghum,soybeans, and the like. In such use application can be made preemergentto both crops and weeds, or, preferably by means of a directed sprayapplication technique, postemergent to the crop plant but bothpreemergent and postemergent to the weeds. In another application, thecompounds can be used to give broad herbicidal action on non-crop land,including intermittently non-crop strips of contour-farmed land. Forsuch usage on so-called fallow land, application can be made in springto suppress vegetative growth until a fall or following spring planting,or in the fall to suppress vegetative growth until a spring or followingfall planting. Furthermore, in another application, the presentcompounds can be utilized to control weeds in tree crop plantings, suchas plantings of the various citrus trees. In all of these variousapplications, and yet others for which the present compounds are suited,another advantage is that the compounds need not be disced into the soilbeing treated, it being adequate if one of the compounds, or aformulation containing one of the compounds, is merely spread onto thetop surface. However, where desired or convenient, the compounds can bedisced into, or otherwise mechanically mixed with the soil. In additionto the foregoing terrestrial embodiments, the present compounds can alsobe utilized as aquatic herbicides.

The practice of the present invention in any of its numerous embodimentscan in some instances be carried out with unmodified compound; however,for good results, it is generally necessary that the compound beemployed in modified form, that is, as one component of a compositionformulated to implement the plant growth-inhibiting effects. Thus, forexample, the active agent can be mixed with water or other liquid orliquids, preferably aided by the usage of a surface active agent. Theactive agent can also be incorporated on a finely divided solid, whichcan be a surface active substance, to yield a wettable powder, which cansubsequently be dispersed in water or other liquid, or incorporated aspart of a dust which can be applied directly. Other methods offormulations are known in the art and can be employed in implementingthe present invention.

In carrying out the novel method of the present invention, the exactamount of the active agent employed is not critical and will vary,depending upon the type of growth-inhibiting effect desired, theidentity of the plants concerned, the particular active agent used,weather conditions, and the like. In general, a broad growth-inhibitingeffect is obtained with rates of from 0.5 to 20 pounds or more of activeagent per acre, and such rates are suitable and effective for control ofvegetative growth on fallow land. When it is desired to obtain aselective growth-inhibiting effect on weeds in areas containing cropplants such as corn, soybeans, and cotton, rates of from 0.25 to 5pounds generally give good results. When in the typical mode ofoperation, the active agent is employed as a composition comprising theagent, the exact concentration of active agent in the composition is notcritical, except that the concentration and total amount of formulationemployed be adequate to supply the appropriate amount of active agent ona per acre basis. In general, good results are obtained when employingformulations containing the active agent in a concentration of from 0.5to 10 percent or higher, in the instance of a liquid formulation; and ina concentration of from 1.0 to 5.0 percent or higher, in the instance ofa dust, powder, granule, or the like. More concentrated formulations canbe prepared and are often preferred in that they can serve, dependingupon the particular application contemplated and the particularconcentration, both as a concentrated formulation for purposes ofshipment, storage, and the like, and as an ultimate treatingcomposition. Thus, for example, formulations often preferably contain asurface active agent and the present active agent, the latter beingpresent in an amount of from 0.5 to 99.5 percent, by weight; or aninert, finely divided solid and the present active agent, the latterbeing present in an amount of from 1.0 to 99.0 percent, by weight. Suchformulations, as indicated, can be employed directly in certainapplications, but can also be diluted and subsequently employed in manyother applications.

Liquid compositions containing the desired amount of active agent areprepared by dissolving the substance in a liquid, with or without theaid of a surface active dispersing agent such as an ionic or non-ionicemulsifying agent. Most preferably, the subject compound in acidic formis dissolved in a dilute aqueous solution of a base, such as, i.e.,sodium hydroxide, whereby a water soluble salt is prepared in solution.Although the use of an organic liquid carrier is seldom preferred inview of the foregoing, it can be used in conjunction with a surfaceactive dispersing agent. When so used, suitable such liquids includeagricultural spray oils and the petroleum distillates such as dieselfuel, kerosene, fuel oil naphthas and Stoddard solvent. The choice ofdispersing and emulsifying agent and the amount thereof employed isdictated by the nature of the composition and by the ability of theagent to facilitate the dispersion of the active agent in the carrier toproduce the desired composition. Dispersing and emulsifying agents whichcan be employed in the compositions include the condensation products ofalkylene oxides with phenols and organic acids, alkyl aryl sulfonates,polyoxyalkylene derivatives or sorbitan esters, complex ether alcohols,and the like. Representative surface active agents which are suitablyemployed in implementing the present invention are identified in U.S.Pat. Nos. 3,095,299, second column, lines 25-36, 2,655,447, column 5,and 2,412,510, columns 4 and 5.

In the preparation of dust compositions, the active ingredient isintimately dispersed in and on a finely divided solid such as clay,talc, chalk, gypsum, limestone, vermiculite fines, perlite, and thelike. In one method of achieving such dispersion, the finely dividedcarrier is mechanically mixed or ground with the active agent.

Similarly, dust compositions containing the toxicant compounds can beprepared with various of the solid surface active dispersing agents suchas bentonite, fuller's earth, attapulgite and other clays. Dependingupon the proportions of ingredients, these dust compositions can beemployed as concentrates and subsequently diluted with additional solidsurface active dispersing agents or with chalk, talc, or gypsum and thelike to obtain the desired amount of active ingredient in a compositionadapted to be employed for the suppression of the growth of the plants.Also, such dust compositions can be dispersed in water, with or withoutthe aid of a dispersing agent, to form spray mixtures.

Formulations containing the present active agent are oftenadvantageously further modified by incorporation therein of an effectiveamount of a surfactant which facilitates the dispersion and spreading ofthe formulation of the plant leaf surfaces and the incorporation of theformulation by the plant.

In accordance with the present invention, the active agent can bedispersed in soil or other growth media in any convenient fashion.Applications can be carried out by simply mixing with the media, byapplying to the surface of soil and thereafter dragging or discing intothe soil to the desired depth, or by employing a liquid carrier toaccomplish the penetration and impregnation. The application of sprayand dust compositions to the surface of soil, or to plant parts or theabove ground surfaces of plants can be carried out by conventionalmethods, e.g., powder dusters, boom and hand sprayers and spray dusters,whether surface or air-borne. However, while such conventional modes ofapplication can be used, they are not required. As above noted, it is anadvantage of the present invention that the compounds serving as activeagent are active and effective as herbicides when merely placed on thesurface of the soil, without any additional step to assistincorporation. Thus, the compounds are of substantially the sameefficacy regardless of whether they are applied to the surface only, orwhether they are applied to the surface and subsequently disced into thesoil.

In a further method, the distribution of the active agent in soil can beaccomplished by introducing the agent into the water employed toirrigate the soil. In such procedures, the amount of water is variedwith the porosity and water holding capacity of the soil to obtain adesired depth of distribution of the agent.

In addition, the present method also comprehends the employment of anaerosol composition containing one or more of the present active agentsas an active compound. Such a composition is prepared according toconventional methods wherein the agent is dispersed in a solvent, andthe resultant dispersion mixed with a propellant in liquid state. Suchvariables as the particular agent to be used and the nature of thevegetation which is to be treated will determine the desirability of thesolvent and concentration of the agent therein.

EXAMPLE 48

6-Chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridinebenzylamine salt was prepared as a means of formulation. Moreparticularly, 1 gram of6-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine wassuspended in about 10 milliliters of water and 1 milliliter ofbenzylamine was added. The reaction mixture was evaporated, yielding asyrup containing6-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridinebenzylamine salt. The syrup is useful to be diluted with water to serve,when so diluted, as a spraying composition.

EXAMPLES 49-52

Various of the compounds to be employed as active agent in accordancewith the present invention were evaluated for preemergent application tovarious species of plants. In this evaluation, a soil was preparedconsisting of one part masonry sand and one part shredded top soilblended together in a cement mixer. One gallon of this soil was placedin a 25 × 35 cm. galvanized flat and was patted down with a bench brushuntil level. A three-row marker was used to make 21/2 cm. deep furrowsin approximately two-fifths of the flat. Crop seeds consisting of fourkernels of corn, five cotton seeds and five soybean seeds were placed inthese furrows. A four-row template was then placed on the remaining soiland the indicated approximate numbers of each of the following seedswere planted, one species to each section: foxtail (millet), 80-100seeds; velvetleaf (40-50 seeds); rough pigweed (150-250 seeds); andlarge crabgrass (100-150 seeds).

Sufficient soil was added to cover the entire flat. Thus, the weed seedswere covered to a depth of about 6 mm. and the crop seeds were coveredto a depth of about 3 cm.

In assaying the effect of the composition as preemergent herbicides, aflat prepared as above, taken either on the day of planting or on thenext day, was placed in a chamber equipped with a turntable and an airexhaust. The herbicidal composition, either a spray-type emulsion or awettable powder, was applied to the flat with a modified DeVilbissatomizer hooked to an air source. Twelve and one-half milliliters of thecomposition under test were applied to each flat either on the day ofplanting or the succeeding day. Injury ratings and observations as totype of injury were made eleven to twelve days after treatment. Theinjury rating scale used was as follows:

0--no injury

1--slight injury

2--moderate injury

3--severe injury

4--death When more than one determination was carried out at a givenrate, an average value was calculated for the injury rating. Eachcompound evaluated was formulated as a spray by one of the followingprocedures. In one method the particular compound was wetted by grindingin a mortar with one part of polyoxyethylene sorbitan monolaurate. Fivehundred parts of water were added slowly to the resultant creamy pasteto give an aqueous dispersion with a surfactant concentration of 0.2percent. This dispersion was entirely satisfactory for sprayapplication. In a second procedure the compound was dissolved in onevolume of acetone, and the acetone solution was diluted with nineteenvolumes of water containing 0.1 percent of polyoxyethylene sorbitanmonolaurate.

In the following table setting forth the results of the evaluation,column 1 gives the name of the compound under test; column 2, the ratein pounds per acre at which the compound was applied to the test flat;and the remaining columns, the injury to the particular plant seeds orseedlings as measured by the foregoing scale.

                                      TABLE I                                     __________________________________________________________________________    Injury Rating on Preemergent Treatment                                                                                     Velvet                           Compound    Lbs./Acre                                                                           Corn                                                                             Cotton                                                                            Soybean                                                                            Crabgrass                                                                           Pigweed                                                                            Foxtail                                                                           Leaf                             __________________________________________________________________________    6-Chloro-1-hydroxy-2-                                                                     8     1  2   1    4     4    3   3                                (trifluoromethyl)-1H-                                                         imidazo(4,5-b)pyridine                                                                    4     1  0   0    4     4    3   4                                            2     0  0   0    3     4    3   4                                            1     0  0   0    4     4    3   2                                2,6-Bis(trifluoromethyl)-                                                     1-hydroxy-1H-imidazo-                                                         (4,5-b)pyridine                                                                           8     3  4   3    4     --   4   --                               6-(Methylsulfonyl)-1-                                                         hydroxy-2-(trifluoro-                                                         methyl)-1H-imidazo-                                                           (4,5-b)pyridine                                                                            2*   0  0   2    2     3    2   2                                5-chloro-1-hydroxy-2-                                                                     8     1  --  --   3     3    4   --                               (trifluoromethyl)-1H-                                                         imidazo(4,5-b)pyridine                                                                    2     0  0   0    3     3    2   --                               __________________________________________________________________________     *Not tested at higher rates.                                             

EXAMPLES 53-58

Representative compounds of the present invention were evaluated forpostemergent application to plants including corn and several weedspecies. The evaluation was carried out in accordance with theprocedures of Examples 49-52 except that the test solutions were appliedabout 9-12 days after the preparation and seeding of the flats. Theresults are as set forth in the following table:

                                      TABLE 2                                     __________________________________________________________________________    Injury Rating on Postemergent Treatment                                                                                     Velvet                          Compound     Lbs./Acre                                                                           Corn                                                                             Cotton                                                                            Soybean                                                                            Crabgrass                                                                           Pigweed                                                                            Foxtail                                                                           leaf                            __________________________________________________________________________    2,6-Bis(trifluoro-                                                                         8     4  4   4    4     4    4   4                               methyl)-1-hydroxy-                                                            1H-imidazo(4,5-b)-                                                                         4     4  4   4    4     4    4   4                               pyridine                                                                                   2     4  4   4    4     4    4   4                                            1     1  4   4    4     4    4   4                               6-Methylsulfonyl-1-                                                                         2*   2  4   4    2     4    4   --                              hydroxy-2-(trifluoro-                                                         methyl-1H-imidazo-                                                                         1     1  3   3    2     3    4   --                              (4,5-b)pyridine                                                               7-Chloro-1-hydroxy-2-                                                                      8     1  --  --   2     3    3   --                              trifluoromethyl-1H-                                                           imidazo(4,5-b)pyri-                                                                        4     0  --  --   1     3    1   --                              dine                                                                          6-Methyl-1-hydroxy-2-                                                                      8     1  --  --   3     3    3   1                               (trifluoromethyl)-1H-                                                         imidazo(4,5-b)pyridine                                                        5,7-Dibromo-6-amino-1-                                                                     8     1  --  --   3     3    3   2                               hydroxy-2-(trifluoro-                                                         methyl)-1H-imidazo(4,5-b)-                                                    pyridine                                                                      5,7-Dibromo-6-chloro-1-                                                                    8     1  --  --   4     4    4   3                               hydroxy-2-(trifluoro-                                                         methyl)-1H-imidazo(4,5-b)-                                                    pyridine                                                                      __________________________________________________________________________     *Not tested at higher rates.                                             

As the foregoing examples illustrate, the compounds of the presentinvention are effective herbicides. However, satisfactory results arealse obtained when the active agent of the present invention, or acomposition comprising such active agent, is combined with otheragricultural materials intended to be applied to plants, plant parts, ortheir habitats. Such materials include fertilizers, fungicides,nematocides, insecticides, other herbicides, soil conditioning agents,and the like.

EXAMPLES 59-60

6-Chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine wasevaluated in combination with2-chloro-4-ethylamino-6-isopropylamino-s-triazine and separately incombination with 2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide forthe control of plants. The evaluations were conducted as described inExamples 49-52, except that the rates of compound differed and thespecies were different. The results were as set forth in the followingtables. General herbicidal effect was rated on a scale of 0-10, with 0 =no injury and 10 = death. Observations were also made for the followingother specific phytotoxic effects.

A = abscission of leaves

B = burned

C = chlorosis

D = death

E = epinasty

F = formative effects other than epinasty

G = dark green

I = increased plant growth

L = local necrosis

N = no germination

P = purple pigmentation

R = reduced germination

S = stunting

U = unclassified injury

Where noted, such effects were recorded and also reported in thefollowing tables.

                                      TABLE 3                                     __________________________________________________________________________             Jim-                                                                              Lambs                                                                             Vel-           Mor-                                                                              John-          Large                      Com- Rates                                                                             son-                                                                              Quar-                                                                             vet-   Rag-                                                                              Pig-                                                                              ning                                                                              son Sor-                                                                              Foxtail                                                                              Crab-  Barnyard            pound                                                                              Lbs./A                                                                            weed                                                                              ter leaf                                                                              Corn                                                                             weed                                                                              weed                                                                              glory                                                                             Grass                                                                             ghum                                                                              Millet                                                                            Corn                                                                             grass                                                                             Rice                                                                             Grass               __________________________________________________________________________    A    0.25                                                                              4B  5S  0   0  2S  0   10D 2S  0   0   0  2S  0  0                        0.5 8BS 6S  2S  0  6S  2S  10D 2S  3SB 2S  0  2S  3B 3S                       1.0 9BS 9SB 8BS 0  8BS 6S  10D 8BS 8BS 7SB 0  3S  6B 3S                       2.0 9BS 9BS 10D 3SB                                                                              8BS 6SB 10D 8BS 10D 10D 3SB                                                                              9BS 9B 9BS                 B    0.25                                                                              9BS 9BS 3S  0  5S  9BS 8BS 3S  0   0   0  0   4B 2S                       0.5 9BS 9BS 3S  0  7SB 10D 9BS 0   0   0   0  2S  4B 5SB                      1.0 9BS 9.5BS                                                                             7BS 0  8BS 10D 10D 0   1B  4SB 0  5S  7B 4SB                      2.0 9BS 9.5BS                                                                             10D 0  10D 10D 10D 2S  2B  5SB 0  6BS 8B 8BS                 A + B                                                                              0.25 +                                                                            9BS 9BS 6BS 0  7BS 8BS 9BS 7SB 3S  2S  0  2S  7B 6BS                      0.25                                                                          0.25 +                                                                            9BS 9BS 7BS 0  10D 10D 10D 3S  0   2S  0  4S  5B 7BS                      0.5                                                                           0.25 +                                                                            10D 9.5BS                                                                             10D 0  9BS 10D 10D 3S  2S  7SB 0  6S  9B 9BS                      1.0                                                                           0.25 +                                                                            9BS 9BS 10D 0  10D 10D 10D 4SB 5SB 8BS 0  9BS 10D                                                                              9.5BS                    2.0                                                                      A + B                                                                              0.5 +                                                                             9BS 9BS 9.5BS                                                                             0  9S  10D 10D 2SB 3BS 4SB 0  2S  8B 6BS                      0.25                                                                          0.5 +                                                                             9BS 9BS 9BS 0  10D 10D 10D 3S  3SB 4S  0  4S  8B 9BS                      0.5                                                                           0.5 +                                                                             9.5BS                                                                             9BS 9.5BS                                                                             0  10D 10D 10D 4SB 4S  5S  0  5S  8B 9BS                      1.0                                                                           0.5 +                                                                             9.5BS                                                                             9S  10D 0  10D 10D 10D 8BS 5SB 8BS 0  9BS 10D                                                                              10D                      2.0                                                                      A + B                                                                              1.0 +                                                                             9.5BS                                                                             9SB 9.5BS                                                                             2S 9.5SB                                                                             9SB 10D 9BS 9BS 10D 2S 5SB 10D                                                                              4SB                      0.25                                                                          1.0 +                                                                             9BS 10D 9.8BS                                                                             0  9.5BS                                                                             9.5BS                                                                             10D 10D 8BS 7BS 0  6SB 10D                                                                              9BS                      0.5                                                                           1.0 +                                                                             10D 10D 9.5BS                                                                             1S 10D 10D 10D 8BS 9BS 10D 0  9BS 10D                                                                              9.5BS                    1.0                                                                           1.0 +                                                                             9BS 9SB 10D 2S 10D 10D 10D 9.5BS                                                                             10D 10D 1S 7SB 10D                                                                              9.5BS                    2.0                                                                      A + B                                                                              2.0+                                                                              10D 9.5SB                                                                             9.8BS                                                                             3S 10D 9.5BS                                                                             10D 9.5BS                                                                             10D 10D 2S 9.5BS                                                                             10D                                                                              9.5BS                    0.25                                                                          2.0 +                                                                             10D 9SB 10D 4S 10D 10D 10D 9SB 10D 10D 4S 9SB 10D                                                                              9.5BS                    0.5                                                                           2.0 +                                                                             9.8BS                                                                             10D 9.5BS                                                                             4S 10D 10D 10D 9.5BS                                                                             10D 10D 3S 10D 10D                                                                              10D                      1.0                                                                           2.0 +                                                                             10D 10D 10D 4S 10D 10D 10D 9.5BS                                                                             9.8BS                                                                             10D 2S 9.5BS                                                                             10D                                                                              10D                      2.0                                                                      (Control)                                                                          0   0   0   0   0  0   0   0   0   0   0   0  0   0  0                   __________________________________________________________________________     A = 6-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine          B = 2-chloro-4-ethylamino-6-isopropylamino-s-triazine                    

                                      TABLE 4                                     __________________________________________________________________________                 Lambs                                                                             Vel-            Mor-                                                                              John-          Large  Barn-              Com- Rates                                                                             Jimson-                                                                           Quar-                                                                             vet-    Rag-                                                                              Pig-                                                                              ning                                                                              son Sor-                                                                              Foxtail                                                                              Crab-  yard               pound                                                                              Lbs./A                                                                            weed                                                                              ter leaf                                                                              Corn                                                                              weed                                                                              weed                                                                              glory                                                                             Grass                                                                             ghum                                                                              Millet                                                                            Corn                                                                             grass                                                                             Rice                                                                             Grass              __________________________________________________________________________    A    0.25                                                                              2B  7RS 0   0   3S  0   5SB 0   0   0   0  0   0  0                       0.5 5BS 6SB 3S  0   2S  3S  10D 0   4S  2S  0  0   3B 0                       1.0 9BS 6SB 5SB 0   8BS 2S  0D  7SB 8BS 6BS 0  2S  4SB                                                                              2S                      2.0 9BS 8BS 9.5BS                                                                             2S  10D 6BS 10D 10D 10D 10D 3S 7SB 8BS                                                                              9BS                C    0.5 0   --  2S  0   0   7S  0   9RS 3SF 9SBR                                                                              0  8RS 0  5SR                     1.0 3S  5S  3S  0   5S  8SR 2S  9RS 4SF 9RSB                                                                              0  9RS 9RS                                                                              8S                      2.0 4S  10N 6S  2S  7S  10N 2SF 9.5RS                                                                             8SF 9.5RSB                                                                            1SB                                                                              10N 10N                                                                              8RSF                    4.0 5S  10N 3S  2S  8SR 10N 3SF 10N 8SFR                                                                              10D 2S 10N 10N                                                                              9.5RS              A + C                                                                              0.25 +                                                                            8BS 7RS 2S  0   3S  9RS 10D 9.5RS                                                                             4SF 9.5BS                                                                             0  9.5RS                                                                             5S 9RS                     0.5                                                                           0.25 +                                                                            9BS 10N 4S  0   7SR 10N 9BS 10D 6SF 9.5BS                                                                             0  10N 10N                                                                              9.5RS                   1.0                                                                           0.25 +                                                                            9BS 10N 5S  2S  10N 10N 9BS 10D 7SF 10D 0  10D 9.5RS                                                                            9.5RS                   2.0                                                                           0.25 +                                                                            10D 10D 6S  2S  10D 10N 10D 10D 9SF 10D 1S 10N 10N                                                                              10N                     4.0                                                                      A + C                                                                              0.5 +                                                                             9BS 9.5RS                                                                             2S  0   8RS 10N 10D 10D 5SF 10D 0  9.8RS                                                                             6SR                                                                              9RS                     0.5                                                                           0.5 +                                                                             9BS 10N 5SB 1S  5S  10N 10D 10D 8SF 10D 0  9RS 9.5RS                                                                            9.5RS                   1.0                                                                           0.5 +                                                                             9.5BS                                                                             10N 6SB 1S  10N 10N 10D 10D 9SF 10D 0  10N 10N                                                                              9.8RS                   2.0                                                                           0.5 +                                                                             10D 10N 7SB 3S  10N 10N 10D 10D 9.5SF                                                                             10D 1S 10N 10N                                                                              9.8RS                   4.0                                                                      A + C                                                                              1.0 +                                                                             8BS 7SR 8BS 1S  7S  10N 10D 10D 8BSF                                                                              10D 0  8SB 7SB                                                                              10D                     0.5                                                                           1.0 +                                                                             9.5BS                                                                             7S  7BS 1S  8SB 10D 10D 10D 8SBF                                                                              10D 0  9SB 9.5RS                                                                            9.5BS                   1.0                                                                           1.0 +                                                                             9.5BS                                                                             8SR 9BS 2S  10D 10N 10D 10N 9BSF                                                                              10D 1SB                                                                              10D 10D                                                                              10D                     2.0                                                                           1.0 +                                                                             9.5BS                                                                             10D 9.5BS                                                                             4S  10D 10D 10D 10D 9.5BS                                                                             10D 4SB                                                                              10D 10N                                                                              10D                     4.0                                                                      A + C                                                                              2.0 +                                                                             9.5BS                                                                             9RS 9.5BS                                                                             5SB 9S  10N 10D 10D 10D 10D 3S 10D 8BS                                                                              10D                     0.5                                                                           2.0 +                                                                             9.5BS                                                                             10D 10D 4SB 10D 10D 10D 10D 10D 10D 5S 9.5BS                                                                             9RS                                                                              9.5BS                   1.0                                                                           2.0 +                                                                             9.8BS                                                                             10D 10D 4SBC                                                                              10D 10D 10D 10D 8BS 10D 3S 10D 9.5RS                                                                            10D                     2.0                                                                           2.0 +                                                                             10D 10D 10D 3S  10D 10N 10D 10D 9.8BS                                                                             10D 4S 10D 10N                                                                              9.8BS                   4.0                                                                      (Control)                                                                          0   0   0   0   0   0   0   0   0   0   0   0  0   0  0                  __________________________________________________________________________     A = 6-chloro-1-hydroxy-2-(trifluoromethyl)-1H-imidazo(4,5-b)pyridine          C = 2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide                  

Essentially the same results as those reported in foregoing Examples49-60 are obtained when evaluating the other representative compounds ofthe present invention identified in Examples 1-48.

The substituted-3-nitro-2-aminopyridine which are employed as startingmaterials in the first synthetic route: ##STR10## are in generalprepared by known procedures. Most typically, the compounds are preparedby nitration, in standard procedures, of suitably substituted pyridineswhich are known or are prepared in procedures readily available to thoseskilled in the art. Thus, for example, in synthesizing5-(difluorochloromethyl)-2-aminopyridine, a 2-aminoformylpyridine:##STR11## is reacted with SF₄ to obtain5-(difluoromethyl)-2-aminopyridine; this compound, in turn, can bechlorinated to obtain the corresponding5-(difluorochloromethyl)-2-aminopyridine. The5-(trifluoromethyl)-2-aminopyridine is synthesized by treatment of5-carboxy-2-hydroxypyridine with SF₄ in the presence of HF, to yield5-(trifluoromethyl)-6-fluoro-5,6-dihydro-2-hydroxypyridine, which, ontreatment with sodium hydroxide, yields5-(trifluoromethyl)-2-hydroxypyridine. The hydroxy moiety of thiscompound can be converted in standard procedures to an amino group, thusyielding the desired 5-(trifluoromethyl)-2-aminopyridine compound.

Preferred starting materials for utilization in the first syntheticroute are the mono-substituted 3-nitro-2-aminopyridines.

Those substituted-3-nitro-2-aminopyridine compounds wherein thesubstituent is alkylsulfonyl: ##STR12## are prepared in accordance withthe following reaction scheme: for the sake of simplicity, the scheme isshown for the preparation of a 5-alkylsulfonyl compound, only. ##STR13##

The following example illustrates the preparation of the(alkylsulfonyl)-3-nitro-2-aminopyridine compounds.

EXAMPLE 61 5-(METHYLSULFONYL)-3-NITRO-2-AMINOPYRIDINE

5-Chloro-2-nitropyridine (8.0 grams) was added to a solution of 2.5grams of sodium methanethiolate in 100 milliliters of ethanol at atemperature of 0° C. to which solution excess sodium methanethiolate wasadded portionwise. The resulting reaction mixture was then heated toreflux and refluxed for 15 hours with constant stirring. At the end ofthe 15 hours, the reaction mixture was filtered and allowed toconcentrate to 75 milliliters. The reaction mixture was then permittedto cool and filtered again, yielding the desired5-(methylthio)-2-nitropyridine; it was recrystallized from ethanol,m.p., 100.5°-02.5° C.

To 3.4 grams of the 5-(methylthio)-2-nitropyridine in 50 milliliters ofglacial acetic acid there was added 23.8 grams of 30 percent hydrogenperoxide. The resulting reaction mixture was stirred for 60 hours at 25°C., then poured over ice and filtered to separate the desired5-(methylsulfonyl)-2-nitropyridine product, which, afterrecrystallization from ethanol/acetone, melted at 165°-7° C.

The entire yield of 5-(methylsulfonyl)-2-nitropyridine (3.2 grams) wasdissolved in about 100 milliliters of acetone and 1 teaspoon of Raneynickel slurry in ethanol added. The mixture was then shaken on a Parrhydrogenator for 15 hours at 60 p.s.i. Thereafter, the mixture wasfiltered and solvent evaporated, yielding the desired5-(methylsulfonyl)-2-aminopyridine product. It was mixed with hot watercontaining some charcoal, filtered and the mixture then cooled to 25° C.The resulting solid was crystallized from benzene/acetone, m.p.,132°-34° C.

5-(Methylsulfonyl)-2-aminopyridine (1.0 gram) was dissolved in 10milliliters of concentrated sulfuric acid and 2.0 milliliters of fumingnitric acid added dropwise with stirring, and the resulting reactionmixture stirred an additional 10 minutes, warmed on a steam bath for 10minutes, and allowed to stir at 25° C. for 15 hours. The reactionmixture was then poured over ice with stirring. Precipitation occurred,and the mixture was filtered to separate5-(methylsulfonyl)-3-nitro-2-hydroxypyridine; it was washed with waterand recrystallized from ethanol/acetone, m.p., 229°-32° C.

5-(Methylsulfonyl)-3-nitro-2-hydroxypyridine (2.0 grams) was mixed with25 milliliters of thionyl chloride and 1 milliliter of dimethylformamideand the mixture refluxed for 2 hours. The reaction mixture was thenevaporated to separate 5-(methylsulfonyl)-3-nitro-2-chloropyridine. Itwas shaken with water to remove any traces of thionyl chloride, and thenfiltered and mixed with 50 milliliters of ammonium hydroxide. Thismixture was stirred, at room temperature, for 15 hours, then poured intoice water and filtered to separate5-(methylsulfonyl)-3-nitro-2-aminopyridine. It was recrystallized fromethanol/acetone, m.p., 239°-41° C.

Analysis, Calc.: C, 33.19; H, 3.25; N, 19.35. Found: C, 33.32; H, 3.31;N, 19.18.

In like manner are prepared the other(alkylsulfonyl)-3-nitro-2-aminopyridine compounds:

6-(ethylsulfonyl)-3-nitro-2-aminopyridine;

5-(isopropylsulfonyl)-3-nitro-2-aminopyridine;

4-(n-propylsulfonyl)-3-nitro-2-aminopyridine;

5-(n-butylsulfonyl)-3-nitro-2-aminopyridine;

6-(isobutylsulfonyl)-3-nitro-2-aminopyridine;

5-(sec-butylsulfonyl)-3-nitro-2-aminopyridine; and

5-(tert-butylsulfonyl)-3-nitro-2-aminopyridine.

Intermediates in the preparation of these compounds include thefollowing:

6-(ethylthio)-2-nitropyridine

5-(n-butylthio)-2-nitropyridine

4-(n-propylsulfonyl)-2-nitropyridine

5-(isobutylsulfonyl)-2-aminopyridine

6-(isopropylsulfonyl)-3-nitro-2-hydroxypyridine

5-(sec-butylsulfonyl)-3-nitro-2-chloropyridine

6-(ethylsulfonyl)-3-nitro-2-chloropyridine

5-(tert-butylsulfonyl)-3-nitro-2-aminopyridine

6-(ethylsulfonyl)-3-nitro-2-aminopyridine

Preferred compounds of the present invention are those mono-substitutedcompounds of the formula ##STR14## wherein R^(1a) represents hydrogen,chlorine, fluorine, difluoromethyl, or trifluoromethyl, and R^(2a)represents halogen, nitro, --CF₃, --CF₂ Cl, --CF₂ H, orloweralkylsulfonyl of C₁ -C₄. Yet more preferred compounds are those ofthe foregoing formula wherein the R^(2a) substituent is located at the6-position, i.e., compounds of the formula ##STR15## wherein R^(1a) andR^(2a) are as above defined.

Other preferred compounds of the present invention are those of theformula ##STR16## wherein each halogen and R^(1a) are as definedhereinabove, and m is 2 or 3. Yet more preferred compounds are those ofthe foregoing formula wherein the halogen is chlorine, bromine, orfluorine; and even more preferred are those wherein the halogen ischlorine. Additional examples of these preferred compounds follow.

5,6-Dichloro-2-amino-3-nitropyridine was prepared by chlorination of5-chloro-2-amino-3-nitropyridine and was subsequently reacted with2,2,3,3-tetrafluoropropionyl chloride. More particularly,5,6-dichloro-2-amino-3-nitropyridine (3.0 grams; 0.15 mole) was taken upin tetrahydrofuran (20 ml.) and triethylamine (2 ml.) was added. Then2,2,3,3-tetrafluoropropionyl chloride was added portionwise until allthe starting material had reacted. The reaction yielded 5.3 grams (94percent yield) of5,6-dichloro-2-(2,2,3,3-tetrafluoropropionamido)-3-nitropyridine as anoil. Its identity was confirmed by infrared spectroscopy.

The 5,6-dichloro-2-(2,2,3,3-tetrafluoropropionamido)-3-nitropyridine(all 5.3 grams; 0.16 mole) was taken up in ethanol (100 ml.) and 1 gramof 5 percent palladium on carbon and 2 ml. of aqueous concentrated HClwere added. The reaction mixture was hydrogenated, filtered, andevaporated. The residue was taken up in 60°-70° petrol and ether,boiled, and filtered. TLC showed a single spot. The1-hydroxy-5,6-dichloro-2-(1,1,2,2-tetrafluoroethyl)-1H-imidazo(4,5-b)pyridineso obtained melted at 183°-184° C.

Analysis, Calc.: C, 31.60; H, 0.99; N, 13.82. Found: C, 31.89; H, 1.20;N, 13.59.

In like procedures, 5,6-dichloro-2-amino-3-nitropyridine was reactedwith trifluoroacetyl chloride and the resulting5,6-dichloro-2-trifluoroacetamido-3-nitropyridine was hydrogenated toobtain1-hydroxy-5,6-dichloro-2-trifluoromethyl-1H-imidazo(4,5-b)-pyridine,m.p. 207°-208° C.

1-Hydroxy-5,6-dichloro-2-(1,1,2,2-tetrafluoroethyl)-1H-imidazo(4,5-b)pyridinewas evaluated in the procedures reported in Examples 49-52. The resultswere as follows:

                  Table 5                                                         ______________________________________                                        Injury Rating on Pretemergent Treatment                                       ______________________________________                                        Lbs./               Soy-  Crab- Pig-  Fox-  Velvet-                           Acre Corn   Cotton  bean  grass weed  tail  leaf                              ______________________________________                                        8    0      --      --    2B    3BS   1S    3B                                4    0      0       1B    2BS   3BS   1BS   1B                                2    0      0       0     1BS   3BS   0     1B                                1    0      0       0     0     1S    0     0                                 ______________________________________                                    

As noted above, the compounds which are the subject of the presentapplication are generally of low mammalian toxicity. However, thecompounds exhibit the unique type of toxicity which makes them suitablefor use as rodenticidal agents. The use of the compounds as rodenticidalagents is disclosed and claimed in copending application Ser. No.517,265, filed Oct. 23, 1974, and issued Mar. 2, 1976, as U.S. Pat. No.3,941,882. Application Ser. No. 517,265 is incorporated herein byreference thereto.

As disclosed in application Ser. No. 517,265, those compounds which beara single substituent located at the 6-position are believed to beoperative through a mechanism of anti-coagulation. The remainder of thecompounds apparently do not share the anti-coagulant mechanism but theprecise mechanism of these compounds is not understood.

Therefore, the preferred compounds which are of the formula ##STR17##are useful as rodenticidal agents, but are operative by a mechanismother than anti-coagulation.

We claim
 1. A compound of the formula ##STR18## wherein R^(1a)represents hydrogen, chlorine, fluorine, difluoromethyl, ortrifluoromethyl; and m is 2 or
 3. 2. A compound of claim 1 wherein eachhalogen is independently bromine, chlorine, or fluorine.
 3. A compoundof claim 1 wherein both or all halogens are chlorine.
 4. The compound ofclaim 3 which is1-hydroxy-5,6-dichloro-2-trifluoromethyl-1H-imidazo(4,5-b)pyridine. 5.The compound of claim 3 which is1-hydroxy-5,6-dichloro-2-pentafluoroethyl-1H-imidazo(4,5-b)pyridine. 6.The compound of claim 3 which is1-hydroxy-5,6-dichloro-2-(1,1,2,2-tetrafluoroethyl)-1H-imidazo(4,5-b)pyridine.